单独删除std::vector <std::vector<string> > 的所有元素

下面为测试代码：

1.创建

std::vector< std::vector<string> > vc2;

2.初始化

    std::vector<string> vc;
    vc.push_back("v11");
    vc.push_back("v12");
    vc.push_back("v13");
 
    std::vector<string> v2;
    v2.push_back("v21");
    v2.push_back("v22");
    v2.push_back("v23");
 
    std::vector<string> v3;
    v3.push_back("v21");
    v3.push_back("v22");
    v3.push_back("v23");
 
    vc2.push_back(vc);
    vc2.push_back(v2);
    vc2.push_back(v3);

3.执行删除操作

    for (std::vector<std::vector<string> >::iterator i = vc2.begin(); i != vc2.end();) {
        for (std::vector<string>::iterator j = i->begin(); j != i->end(); ) {
            j = i->erase(j);
        }
        i = vc2.erase(i);
    }